A method for preparing a manganese-based prussian blue analogue

Abstract

The application discloses a preparation method of a manganese-based Prussian blue analogue, which comprises the following steps: ①carrying out a pre-complexation reaction on a manganese source and an organic ligand in anhydrous organic solvent I; ②adding a manganese-based complex precursor prepared in the step ①, ferrocyanide and a sodium source into anhydrous organic solvent II to obtain a reaction system; ③carrying out a pre-reaction treatment on the reaction system obtained in the step ② for 1-10 hours; and ④carrying out a solvothermal reaction on the material after the pre-treatment in the step ③ under a closed condition, wherein the solvothermal reaction temperature is 150-250 DEG C, and the reaction time is 6-24 hours, and a Prussian blue analogue material is obtained through the reaction.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a method for preparing a manganese-based Prussian blue analogue for sodium-ion battery cathode materials. Background Technology

[0002] In modern energy systems, developing cost-effective energy storage technologies has become a key challenge in promoting the utilization of renewable energy and the development of smart grids. While lithium-ion batteries (LIBs) have achieved significant success since their commercialization, their large-scale application faces fundamental limitations: lithium's abundance in the Earth's crust is relatively low (approximately 0.0065%) and its geographical distribution is uneven. In contrast, sodium-ion batteries (SIBs) have regained attention due to their unique elemental properties and electrochemical advantages, and are considered a potential alternative to large-scale grid-connected energy storage systems. Sodium not only has a higher abundance in the Earth's crust (approximately 2.36%), but its physicochemical properties are also similar to lithium, giving sodium-based electrochemical energy storage technologies significant advantages in terms of cost-effectiveness and sustainability.

[0003] The molecular formula is A x M[Fe(CN)6] y Prussian blue analogues (PBAs) of zH₂O (0 ≤ x ≤ 2, y ≤ 1, A = alkali metal, M = Mn, Fe, Co, Ni) have become one of the most promising cathode materials for sodium-ion batteries (SIBs) due to their unique double perovskite open-framework structure. This structure is beneficial for Na… + Highly efficient insertion and extraction. When A is Na and M is Mn, it is manganese-based Prussian white. Due to its high sodium content, it appears white and is therefore called Prussian white.

[0004] Among numerous transition metal-based PBA materials, those based on Fe... 2+ / Fe 3+ While iron-based redox couples are relatively inexpensive, they have relatively low operating voltages; cobalt-based materials exhibit excellent electrochemical performance but are expensive; and nickel-based materials demonstrate electrochemical inertness. In contrast, manganese-based PBA materials show significant advantages: not only are they moderately priced, but they can also operate at 3.45 V (vs Na / Na) + It provides up to 170 mAh g at a high average operating voltage. -1 Its theoretical specific capacity is comparable to that of commercial lithium-ion battery cathode materials, demonstrating great application potential.

[0005] However, manganese-based Prussian blue analogues still face some key challenges in practical applications. For example, these materials often contain significant amounts of crystal water and coordination water, which can easily lead to the formation of lattice defects, thus affecting the material's structural stability and cycling performance. Furthermore, the Jahn-Teller effect of Mn³⁺ ions can easily cause crystal structure distortion, further impacting the material's electrochemical stability. Therefore, reducing the water content and improving the structural integrity and crystallinity of these materials through rational synthesis methods is a crucial research direction for this class of materials.

[0006] Regarding the preparation method of manganese-based Prussian blue analogues, Chinese patent document CN 117430135 A (application number 202311767283.8) discloses a method for synthesizing manganese-iron-based Prussian blue sodium electrode material by grinding, including the following steps: (1) mixing sodium ferrocyanide, elemental manganese powder and solid organic acid with a molar ratio of 1:0.5~3:0.6~3.6 with a polar organic solvent, wherein the total mass ratio of sodium ferrocyanide, elemental manganese powder and solid organic acid to the mass ratio of polar organic solvent is 10:1~10; (2) ball milling the raw materials after step (1) under closed conditions to obtain a mixture; (3) washing the mixture obtained in step (2) with deionized water and anhydrous ethanol, and vacuum drying the washed product to obtain manganese-iron-based Prussian blue sodium electrode material. Summary of the Invention

[0007] The technical problem to be solved by the present invention is the high water content and structural stability of manganese-based Prussian blue analogs. The present invention provides a method for preparing manganese-based Prussian blue analogs with low water content, regular grain morphology and high crystallinity.

[0008] The technical solution for achieving the objective of this invention is a method for preparing a manganese-based Prussian blue analogue, comprising the following steps: ① A manganese source and an organic ligand were subjected to a pre-complexation reaction in anhydrous organic solvent I to obtain a manganese-based complex precursor. The molar ratio of the manganese source to the organic ligand was 1:3~4.

[0009] ② Add the manganese-based complex precursor, ferrocyanide, and sodium source prepared in step ① to anhydrous organic solvent II to obtain the reaction system; the molar ratio of ferrocyanide to manganese source in step ① is 1:1~2, and the molar ratio of ferrocyanide to sodium source is 1:8~12.

[0010] ③ Perform a pre-reaction treatment on the reaction system obtained in step ② at 40-100℃ for 1–10 hours.

[0011] ④ The pretreated material from step ③ is subjected to a solvothermal reaction under sealed conditions. The solvothermal reaction temperature is 150-250℃ and the reaction time is 6-24 hours to obtain Prussian blue analog material.

[0012] ⑤ Centrifuge the product obtained in step ④, wash and dry the resulting solid phase to obtain Prussian blue analog material.

[0013] In step ① above, the pre-complexation reaction temperature is 20–80℃, and the reaction time is 0.5–6 hours.

[0014] In step ① above, the manganese source is at least one of anhydrous manganese sulfate, anhydrous manganese nitrate, manganese acetate, and manganese chloride; The organic ligand is at least one of citric acid, sodium citrate, oxalic acid, tartaric acid, and ethylenediaminetetraacetic acid.

[0015] In step ① above, the anhydrous organic solvent I is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

[0016] In step ② above, the sodium source is at least one of sodium chloride, sodium sulfate, or sodium carbonate; The ferrocyanide is at least one of sodium ferrocyanide or sodium ferrocyanide decahydrate.

[0017] In step ② above, the anhydrous organic solvent II is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

[0018] Alternatively, in steps ① and ②, the anhydrous organic solvent I and anhydrous organic solvent II are the same.

[0019] In step ③ above, the pretreatment reaction is carried out in a vacuum environment of -0.095 to -0.099 MPa.

[0020] In step ④ above, the solvothermal reaction is carried out under a vacuum environment of -0.095 to -0.099 MPa. This invention has the following positive effects: The preparation method of this invention uses an anhydrous organic solvent as the reaction medium at high temperature (150-250℃) to promote crystal growth through a homogeneous reaction at the molecular level, thereby obtaining a manganese-based Prussian blue analogue, namely manganese-based Prussian white (Na). x Mn[Fe(CN)6] y· nH2O; where 1.0<x≤2, 0<y≤1, 0<n≤10); the resulting grains have regular morphology and high crystallinity, and the product has high purity.

[0021] This invention involves a reaction conducted in a high-temperature, anhydrous, and sealed environment, which effectively isolates the intrusion of moisture in the air and prevents water molecules from entering the crystal lattice.

[0022] The solvothermal reaction conditions of this invention are conducive to crystal growth, thereby improving the crystallinity and structural integrity of the material.

[0023] The manganese-based Prussian blue analogue prepared by this invention has a stable structure, which is beneficial for improving the cycle performance of sodium-ion batteries.

[0024] The present invention has a simple process and a short reaction time, and has good prospects for industrial application. Attached Figure Description

[0025] Figure 1 The X-ray diffraction pattern of manganese-based Prussian white prepared in Example 1.

[0026] Figure 2 The rate performance diagram is for the manganese-based Prussian white prepared in Example 1.

[0027] Figure 3 The image shows the cycling performance of the manganese-based Prussian white prepared in Example 1.

[0028] Figure 4 The voltage-to-capacity curve of the manganese-based Prussian white prepared in Example 1.

[0029] Figure 5 This is a comparison chart of the magnification of Example 1 and Comparative Example 1. Detailed Implementation

[0030] The following describes some of the possible embodiments of the present invention, intended to provide a basic understanding of the invention, and is not intended to identify the key or decisive elements of the invention or limit the scope of protection. It is readily understood that, based on the technical solutions of the present invention, those skilled in the art can propose other interchangeable implementations without altering the essential spirit of the invention. Therefore, the following specific embodiments are merely illustrative examples of the technical solutions of the present invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solutions of the present invention.

[0031] In manganese-based Prussian blue analogues (PBA), the manganese ion's ginger-Taylor effect... Jahn-Teller The α-effect easily induces crystal structure distortion, while the material itself has low intrinsic conductivity. These factors together weaken the structural stability of manganese-based PBA, resulting in poor cycle performance and severely restricting the practical large-scale application of this material in the field of energy storage.

[0032] To overcome the aforementioned defects in existing technologies and improve battery storage capacity, this invention provides a method for preparing Prussian blue analogues for sodium-ion battery cathodes using a solvothermal reaction without the participation of water.

[0033] The preparation method of the present invention includes the following steps: ① A manganese source and an organic ligand were subjected to a pre-complexation reaction in anhydrous organic solvent I to obtain a manganese-based complex precursor; the pre-complexation reaction temperature was 20–80℃ and the reaction time was 0.5–6 hours.

[0034] The molar ratio of manganese source to organic ligand is 1:3-4.

[0035] The mass of anhydrous organic solvent I is 2-6 times the total mass of the solute (total mass of manganese source and organic ligand).

[0036] The manganese source is at least one of anhydrous manganese sulfate, anhydrous manganese nitrate, manganese acetate, and manganese chloride.

[0037] The organic ligand is at least one of citric acid, sodium citrate, oxalic acid, tartaric acid, and ethylenediaminetetraacetic acid.

[0038] The water content of the anhydrous organic solvent is less than 1 wt% (the same applies below).

[0039] Anhydrous organic solvent I is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

[0040] Specifically, the pre-complexation reaction temperature can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, or 80℃, or any value can be selected between any two of the above temperature values.

[0041] Specifically, the reaction time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h, or any duration can be selected between any two of the above values.

[0042] ② The manganese-based complex precursor, ferrocyanide, and sodium source prepared in step ① are added to anhydrous organic solvent II to obtain the reaction system.

[0043] The molar ratio of ferrocyanide to manganese source in step ① is 1:1-2.

[0044] The molar ratio of ferrocyanide to sodium source is 1:8-12.

[0045] The amount of anhydrous organic solvent II is 1-4 times the total mass of the solute in step ② (total mass of manganese complex precursor, ferrocyanide and sodium source).

[0046] The sodium source is at least one of sodium chloride, sodium sulfate, or sodium carbonate.

[0047] The ferrocyanide is at least one of sodium ferrocyanide or sodium ferrocyanide decahydrate.

[0048] The anhydrous organic solvent has a water content of less than 1 wt%. Anhydrous organic solvent II is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

[0049] Alternatively, the anhydrous organic solvents I and II used in steps ① and ② can be the same.

[0050] ③ The reaction system obtained in step ② is subjected to pre-reaction treatment for 1–10 hours under vacuum conditions (-0.095 to -0.099 MPa) and 40–100℃ to allow manganese ions to be gradually released in a complexed state and form an initial nucleation structure.

[0051] Specifically, the pre-reaction temperature can be 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, or 100℃, or any value between any two of the above temperature ranges can be selected.

[0052] Specifically, the pre-reaction treatment time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or any duration between any two of the above values ​​can be selected.

[0053] ④ The pretreated material from step ③ is subjected to a solvothermal reaction under vacuum and sealed conditions. The solvothermal reaction temperature is 150-250℃, and the reaction time is 6-24 hours. Prussian blue analogue material is obtained.

[0054] Specifically, the solvothermal reaction temperature can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃, or any value can be selected between any two of the above temperature values.

[0055] Specifically, the reaction time can be 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h, or any value can be selected from any of the above time values.

[0056] ⑤ The obtained product was centrifuged and the resulting solid phase was washed three times with anhydrous organic solvent III to remove unreacted precursors and byproducts; then the product was dried in a drying oven to obtain manganese-based Prussian white sodium-ion battery cathode material with low water of crystallization content.

[0057] The anhydrous organic solvent III is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

[0058] Preferably, the drying can be carried out in a vacuum or inert gas environment.

[0059] The specific implementation method is as follows.

[0060] (Example 1) The manganese-based Prussian blue analogue prepared in this embodiment is manganese-based Prussian white.

[0061] The preparation method of manganese-based Prussian white in this embodiment includes the following steps: ① Add 0.755 g (0.0050 mol) of anhydrous manganese sulfate and 4.8526 g (0.0165 mol) of sodium citrate dihydrate to 20 mL of anhydrous acetonitrile and react at 80 °C for 4 hours to pre-complex and obtain the manganese-based complex precursor.

[0062] ② Add the manganese-based complex precursor prepared in step ①, 1.52 g (0.005 mol) of anhydrous sodium ferrocyanide and 2.922 g (0.05 mol) of sodium chloride to 40 mL of acetonitrile to obtain the reaction system.

[0063] ③ Transfer the reaction system to a vacuum drying oven, turn on the vacuum pump to evacuate to -0.095 to -0.099 MPa, and perform a constant temperature pre-reaction treatment on the reaction system obtained in step ② for 8 hours under vacuum conditions and 80℃, so that manganese ions are gradually released in a complex state and form an initial nucleation structure.

[0064] ④ Transfer the pretreated material from step ③ to a hydrothermal reactor, place it in a vacuum drying oven, and heat it at 170℃ under vacuum for 10 h to obtain the product.

[0065] ⑤ The obtained product was centrifuged and the solid phase was washed three times with anhydrous ethanol to remove unreacted precursors and byproducts; then the product was placed in a vacuum drying oven and dried at 80°C for 10 h to obtain 0.974 g of manganese-based Prussian white sodium-ion battery cathode material with low water of crystallization content.

[0066] The X-ray diffraction pattern of the obtained manganese-based Prussian white is shown in the figure. Figure 1 .Depend on Figure 1 It can be seen that the sharp peaks and small half-peak widths of the XRD pattern indicate that the material has high crystallinity and good crystal structure integrity; the high intensity of the diffraction peaks and the stable baseline without broadening or bulging indicate that the material has few amorphous impurities and high crystal phase purity.

[0067] (Example 2) The preparation method in this embodiment is otherwise the same as in Example 1, except that: The anhydrous organic solvent in steps ① and ② is N,N-dimethylformamide.

[0068] (Example 3) The preparation method in this embodiment is otherwise the same as in Example 1, except that: The anhydrous organic solvent in steps ① and ② is ethanol.

[0069] (Example 4) The preparation method in this embodiment is otherwise the same as in Example 1, except that: In step ①, 0.005 mol of anhydrous manganese sulfate and 0.0155 mol (2.33 g) of tartaric acid were added to 20 mL of anhydrous acetonitrile and reacted at 40 °C for 4 hours to pre-complex and obtain the manganese-based complex precursor.

[0070] (Example 5) The preparation method in this embodiment is otherwise the same as in Example 1, except that: In step ②, the sodium source is sodium carbonate.

[0071] (Comparative Example 1) Solution A was prepared by dissolving 2.922 g (0.05 mol) of sodium chloride in 50 mL of deionized water; solution B was prepared by dissolving 1.52 g (0.005 mol) of anhydrous sodium ferrocyanide in 50 mL of deionized water; and solution C was prepared by adding 0.755 g (0.0050 mol) of anhydrous manganese sulfate and 4.8526 g (0.0165 mol) of sodium citrate dihydrate to 50 mL of deionized water. Nitrogen gas was continuously introduced into solution A to maintain an anaerobic environment under continuous stirring and constant temperature heating. Then, solutions B and C were slowly added dropwise to solution A using a peristaltic pump. The resulting white precipitate was thoroughly washed and then dried in a vacuum oven at 80 °C for 12 h under vacuum conditions, finally obtaining the manganese-based Prussian white material prepared by the co-precipitation method.

[0072] (Experimental Example 1) The manganese-based Prussian white, conductive carbon black, and PVDF prepared in Example 1 were mixed at a mass ratio of 7:2:1, ball-milled for 30 min with NMP as solvent to prepare a slurry, which was then coated onto aluminum foil and vacuum-dried at 80 °C for 12 h to obtain the working electrode. A coin cell was then assembled in a glove box.

[0073] An electrochemical testing system was used to perform constant current charge-discharge tests within a set voltage range. Cyclic tests were conducted at different current densities (such as 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, etc.), with several cycles at each rate. The specific capacity change and charge-discharge curves were recorded.

[0074] The measured rate performance graph is shown below. Figure 2 ,Depend on Figure 2As can be seen, this material exhibits good rate performance and cycling stability at different rates. As the rate increases from 0.1C to 5C, the specific capacity gradually decreases, but it still maintains a capacity of approximately 80 mAh g⁻¹ at 5C, indicating good ion transport capability. The capacity recovers upon returning to a lower rate, indicating stable material structure and good reversibility. Meanwhile, the coulombic efficiency remains close to 100%, indicating stable electrochemical reactions and few side reactions.

[0075] See the cycle performance diagram. Figure 3 ,Depend on Figure 3 It is evident that this material exhibits good cycling stability under 5C high-rate conditions. With increasing cycle count, the discharge specific capacity gradually decreases from approximately 75 mAh g⁻¹ to approximately 55 mAh g⁻¹, showing a relatively smooth capacity decay, indicating good structural stability. Simultaneously, the coulombic efficiency remains close to 100%, indicating high reversibility of the electrode reaction and few side reactions, demonstrating excellent high-rate cycling performance.

[0076] See the voltage-to-capacity curve. Figure 4 ,Depend on Figure 4 As shown in the figure, this is the constant current charge-discharge curve of the material at different rates. As the rate increases from 0.1C to 10C, the specific capacity gradually decreases, which is due to enhanced polarization and restricted Na⁺ diffusion at high rates. Meanwhile, there are relatively obvious charge-discharge plateaus at each rate, indicating that the material has a stable redox reaction process. With increasing rate, the voltage difference between charge-discharge plateaus gradually increases, indicating enhanced electrochemical polarization. However, it still maintains a certain capacity under high rate conditions, indicating that the material has good rate performance and structural stability.

[0077] (Experimental Example 2) The manganese-based Prussian white prepared in Example 1 and Comparative Example 1 were mixed with conductive carbon black and PVDF at a mass ratio of 7:2:1, respectively. The mixtures were ball-milled for 30 min using NMP as a solvent to prepare slurries, which were then coated onto aluminum foil and vacuum-dried at 80 °C for 12 h to obtain working electrodes. These electrodes were then assembled into coin cells in a glove box.

[0078] An electrochemical testing system was used to perform constant current charge-discharge tests within a set voltage range. The two working electrodes were cyclically tested at different current densities (such as 0.5C, 1C, 2C, 5C, 10C, etc.). Several cycles were performed at each rate, and the specific capacity change and charge-discharge curves were recorded.

[0079] The ratio comparison chart is as follows Figure 5 ,Depend on Figure 5As can be seen, Example 1 exhibits average discharge specific capacities of 106.3, 101.6, 92.3, 75.5, and 53.4 mAh·g⁻¹ at current rates of 0.5C, 1C, 2C, 5C, and 10C, respectively. In contrast, the electrochemical performance of Comparative Example 1 is significantly lower. Under the same current rates (0.5C, 1C, 2C, 5C, and 10C), its average discharge specific capacities are only 96.3, 78.9, 58.8, 21.2, and 2.3 mAh·g⁻¹, respectively. Especially at the high current rate of 10C, the capacity of Comparative Example 1 is lower, further demonstrating that the material prepared according to the method of this application possesses superior fast sodium ion transport kinetics.

[0080] In summary, the manganese-based Prussian blue analogue prepared by this invention has a stable structure and improves the cycle performance of sodium-ion batteries.

Claims

1. A method for the preparation of a manganese-based Prussian blue analogue, characterized in that Includes the following steps: ① A manganese source and an organic ligand were pre-complexed in an anhydrous organic solvent I to obtain a manganese-based complex precursor. The molar ratio of the manganese source to the organic ligand was 1:3~4. ② Add the manganese-based complex precursor, ferrocyanide and sodium source prepared in step ① to anhydrous organic solvent II to obtain the reaction system; the molar ratio of ferrocyanide to manganese source in step ① is 1:1~2, and the molar ratio of ferrocyanide to sodium source is 1:8~12. ③ Perform a pre-reaction treatment on the reaction system obtained in step ② at 40-100℃ for 1–10 hours; ④ The pretreated material from step ③ is subjected to a solvothermal reaction under sealed conditions. The solvothermal reaction temperature is 150-250℃ and the time is 6-24 hours to obtain Prussian blue analog material. ⑤ Centrifuge the product obtained in step ④, wash and dry the resulting solid phase to obtain Prussian blue analog material.

2. The method for preparing manganese-based Prussian blue analogues according to claim 1, characterized in that: In step ①, the pre-complexation reaction temperature is 20–80℃, and the reaction time is 0.5–6 hours.

3. The method for preparing manganese-based Prussian blue analogues according to claim 1, characterized in that: In step ①, the manganese source is at least one of anhydrous manganese sulfate, anhydrous manganese nitrate, manganese acetate, and manganese chloride; The organic ligand is at least one of citric acid, sodium citrate, oxalic acid, tartaric acid, and ethylenediaminetetraacetic acid.

4. The method for preparing manganese-based Prussian blue analogues according to claim 1, characterized in that: In step ①, the anhydrous organic solvent I is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

5. The method for preparing manganese-based Prussian blue analogues according to claim 1, characterized in that: In step ②, the sodium source is at least one of sodium chloride, sodium sulfate, or sodium carbonate; The ferrocyanide is at least one of sodium ferrocyanide or sodium ferrocyanide decahydrate.

6. The method for preparing manganese-based Prussian blue analogues according to claim 1, characterized in that: In step ②, the anhydrous organic solvent II is at least one of acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and ethanol.

7. The method for preparing the manganese-based Prussian blue analogue according to claim 1, characterized in that: In step ③, the pretreatment reaction is carried out under a vacuum environment of -0.095 to -0.099 MPa.

8. The method of claim 1, wherein: In step ④, a solvothermal reaction is carried out under a vacuum environment of -0.095 to -0.099 MPa.

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